Throttle Valve Lift

Connect tachometer, start engine and increase engine speed to about 2500 RPM. Release accelerator and observe vacuum governor on carburetor. Above 2000 RPM, adjustment screw should contact operating lever of carburetor. Below 1800 RPM, diaphragm should be retracted by vacuum and adjustment screw should not touch lever. If no throttle valve lift is effected during this test, check vacuum connections, RPM switch and switch-over valve.